A suicide bomber targeting a bus of government employees near Kabul's biggest prison has killed at least seven people on Wednesday.

Interior ministry spokesman Najib Danish said the attacker detonated explosives near a vehicle of the employees from Pul-e-Charkhi prison on the outskirts of the Afghan capital. Another five people were wounded in the blast.

There was no immediate claim of responsibility.

The attacker was on foot, Danish said.

The attack comes days after a suicide attack near the entrance of Afghanistan's Independent Election Commission in Kabul, killing at least one person and wounding six.

Afghan civilians continue to be killed in record numbers by anti-government armed groups this year, and the United Nations said the deaths have been the highest since 2014.